Production of pure metals

ABSTRACT

A PROCESS FOR DEPOSITING ELEMENTS BY IRRADIATING LIQUIDS ULTRA PURE ELEMENTS ARE PRECIPITATED FROM AQUEOUS SOLUTIONS OR SUSPENSIONS OF COMPOUNDS. A SOLUTION OF A SALT OF A METAL TO BE PREPARED IS IRRADIATED, AND THE INSOLUBLE REACTION PRODUCT SETTLES OUT. SOME CHEMICAL COMPOUNDS MAY ALSO BE PREPARED IN THE MANNER.

US. Cl. 204157.1 H Claims ABSTRACT OF THE DISCLOSURE A process fordepositing elements by irradiating liquids. Ultra pure elements areprecipitated from aqueous solutions or suspensions of compounds. Asolution of a salt of a metal to be prepared is irradiated, and theinsoluble reaction product settles out. Some chemical compounds may alsobe prepared in this manner.

ORIGIN OF THE INVENTION The invention described herein was made byemployees of the United States Government and may be manufactured andused by or for the Government for governmental purposes without thepayment of any royalties thereon or therefor.

RELATED APPLICATION This application is a continuation-in-part ofcopending application Ser. No. 876,588, filed Nov. 13, 1969, now U.S.Pat. No. 3,658,569.

BACKGROUND OF THE INVENTION This invention is concerned with aradiation-chemical process for depositing high purity elements,particularly metals. The invention is also directed to the separation ofdesired metals from solutions containing several metal compounds.

At the present time there are numerous methods of producing metals. Someof these methods utilize high temperatures. These methods include thedirect reduction of a metal compound with carbon or hydrogen,aluminothermic reactions, and the electrolysis of fused salt systems.

Problems of contamination of the metal product have been encounteredwith these high temperature methods. This contamination is the result ofthe solubility of the container material in the reaction media and/orits diffusion into the media. Contamination can also be caused byreactants, such as carbon or other metals, as well as oxygen or nitrogenwhich are components of the atmosphere because of the strong tendency ofmetals to oxidize at elevated temperatures.

Not only are problems encountered in controlling the conventionalchemical processes to avoid chemical contamination, but also isolationof the metal is difficult to achieve. One disadvantage of theconventional electrochemical process is that it is limited toelectrically conducting solvents.

SUMMARY OF THE INVENTION These problems have been solved by the presentinvention wherein solutions of metal salts or compounds are irradiatedwith high energy particles. This promotes a chemical reaction causingmetals to precipitate, or separate out, from the solutions. The processis performed at room temperature, normal pressure, and under an inertatmosphere.

United States Patent 0" ice Copending application Ser. No. 876,588,filed Nov. 13, 1969, now -U.S. Pat. No. 3,658,569, describes aradiationchemical process for depositing nickel. A substrate isimpregnated with an irradiation sensitive salt and then irradiated tocause a chemical change. Nickel is deposited by immersing the substratein an aqueous developing solution.

The reaction mechanism of the present invention involves a decompositionof the solvent by ionizing radiation. In aqueous systems the speciesformed are hydrogen atoms, hydrated (solvated) electrons, and hydroxylradicals. The hydrogen atoms and hydrated (solvated) electrons arereducing agents while the hydroxyl radicals are oxidizing agents. Ametal can be reduced by the hydrogen atoms or hydrated (solvated)electrons.

OBJECTS OF THE INVENTION It is, therefore, an object of the presentinvention to provide a radiation chemistry method for producing theelements and compounds of high purity as well as improved polymers andnew compounds.

Another object of the invention is to provide a low temperature processfor preparing pure metals from a solution; the temperature being limitedby the freezing point of the solution.

Still another object of the invention is to provide a radiochemicalmethod of producing pure metals in an oxygen and nitrogen-free media.

A further object of the invention is to provide a method of producingadherent metal coatings on substrates as well as the controlleddeposition of materials.

A still further object of the invention is to provide a method forseparating individual metals from solutions containing two or more metalcompounds.

An additional object of the invention is to provide an improved methodof preparing catalysts.

These and other objects and advantages of the invention will be apparentfrom the specification which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENT According to the preferredembodiment of the invention aqueous solutions or suspensions of metalcompounds are irradiated with high energy particles. Such particlesinclude electrons, protons, ions and neutrons obtained from particleaccelerators and radioactive sources.

The present invention is based on the existence of relatively long livedreducing species produced when certain liquids are irradiated. In waterevery electron volts of radiation energy produces about four hydrated(solvated) electrons. Therefore, a single 1 mev. electron from anirradiation source produces about 10 hydrated (solvated) electrons.

The addition of a hydroxyl radical scavenger which reacts rapidly withthe oxidizing hydroxyl radicals (OH) but slowly with the reducinghydrogen atoms (H) and hydrated (solvated) electrons (e generates anoverall reducing system. These hydroxyl radical scavengers includeprimary alcohols, secondary alcohols, polyhydroxyl alcohols, aldehydesand, in general, readily oxidizable organic compounds. Some inorganicreducing agents, such as hypophosphites, H PO may also be used. For manyorganic solvents a scavenger additive is unnecessary.

According to the invention the metal compound is dissolved in anappropriate solvent or mixture of solvents. To illustrate the preferredembodiment of the invention about 500 cubic centimeters of an aqueoussolution containing a metal salt and a scavenger was placed in areaction vessel which was closed to the atmosphere. Irradiation withhigh energy particles in the form of an electron beam furnished by aIDynamitron accelerator was satisfactory. This accelerator is capable ofsupplying agceleratingpotentials between 0.5 and 3.0 million voltstogether with a controllable beam current capability up to 10milliamperes.

, The electron beamentered the vessel through a thin indow, such as .001inch thick titanium foil. A or inert gas passing through fritted glassat fhebottomiofthe vesselprovided stirring of the solution. The gasexited through an'outlet tube near the top of the vessel.

' The contents were maintained at about 20 C. during irradiation byimmersing the reaction vessel in a water batli'.The duration of theaverage run was between one and two hours. The dose, in coulombs, wasobtained from a beam current integrator.

'The product yield, n-G(M), is essentially independent of electronaccelerating voltage between 0.5 and 2.5 mev.

An accelerating voltage of 2 mev. was used for all the runs. Thepenetration of the electrons was about one centimeter, and the diameterof the beam was about four centimeters.

After irradiation, the insoluble product deposited from the aqueoussolution was removed by centrifuging and washed thoroughly with water.The wet powder was then suspended in acetone, filtered in a frittedglass filter, and dried at room temperature for about 12 hours. Thetared filter containing the metal powder was further dried at about 70C. for about 2 hours and weighed. A relatively low drying temperaturewas used to prevent undue atmospheric oxidation of the metal powder.Metal samples used for analysis were vacuum dried at 100 C. instead ofbeing dried in air.

Twelve metals were prepared in this manner by electron irradiation oftheir aqueous salt solution. These metals are listed in Table I.

The yields in Table I for thallium, tin, antimony, iron,

nickel and cobalt were from products prepared from alkaline solutions.Each yield in Table I is first expressed in terms of n-G(M) where n isthe valence change that occurs when the metal ion is reduced to themetal, and G(M) is the number of metal atoms produced for 100 ev.energy. The yield is also expressed in grams per kilowatthour. For avalence change of two, an n-G(M) value of 1 is equivalent to about 0.2mole of metal product per kilowatt-hour of energy into the solution. Inmost cases metal produced radiochemically from the aqueous solutiondeposited as fine powders. The metal powders, especially the more activemetals, are sensitive to atmospheric oxidation. The soft metals,cadmium, tin, and particularly lead form macro sponge-likeconglomerates. When formed by irradiating a solution of an electrolyte,such as lead acetate, some of the lead is colloidal. In such a solutiona lead mirror deposits on the glass reaction vessel. No colloidal leadis formed from a solution of a strong electrolyte, such as leadperchlorate or a base solution containing lead acetate.

Inherent characteristics of the radio-chemical method lead to theproduction of high purity metals. Deposition of metals occurs at a lowenough temperature where contamination due to diffusion of containermaterial and/or reaction with the environment is minimized. The productis isolatedas a precipitate; reactants and unwanted reaction productsremain in solution. Also easily purified metal salts may be used.

Samples of silver, copper and nickel were all found to be 99.9+% pure bychemical analysis. In each metal, X- ray defractionshowed that only themetal was present.

DESCRIPTION OFALTERNATE. EMBODIMENT" Active metals, those which re'ducewater, and anhydrous compounds are best prepared from dry organicliquids. Antimony and some anhydrous lower, valence metalhalides wereprepared in accordance with the invention using dry organic liquids assolvents. Antimony '(III) chl oride (SbCl was selected as the metal saltb'ecauseof its solubility in a wide variety of organic liquids andbecause of the relative convenience in handling antimony metal.

The yield of antimony upon irradiation of SbCl solutions in dry organicliquids is shown'in Table II. As in the preferred embodiment theelectron energy was 2 mev. The concentration of the SbCl was 0.25 M, thecurrent was 20 ,ua., and the dose was 0.20 coulomb.

TABLE II.ANTIMONY YIELD Y While several embodiments of the inventionhave been described it will be appreciated that various modificationsmay be made without departing from the spirit of the invention or thescope of the subjoined claims. For example, other metals including zincand cadmium have also been deposited from dry organic liquids.

What is claimed is:

1. A radiation chemical process for producing pure metals comprising thesteps of adding an oxidizing species scavenger to a liquid whichdecomposes when irradiated with high energy particles producing longlived reducing species and oxidizing species, dissolving at least onemetal compound in said liquid to form a solution, placing said solutionin an inert atmosphere at ambient temperature and pressure, irradiatingsaid solution with high energy particles while in said inert atmosphereat ambient temperature and pressure thereby decomposing said liquidwhereby said oxidizing species are scavenged and at least one metal isreduced and precipitates from said solution as a pure metal, andremoving said pure metal from said solution.

2. A radiation chemical process as claimed in claim 1 wherein a salt ofa metal is dissolved in the solvent and said metal precipitates fromsaid solvent.

3. A radiation chemical process as claimed in claim 1 wherein aplurality of metal compounds are dissolved in the solvent and apredetermined metal precipitates from said solvent.

4. A radiation chemical process as claimed in claim 1 wherein thesolution is irradiated with an electron beam having an acceleratingvoltage between 0.5 and 2.5 mev.

5. A radiation chemical process as claimed in claim 4 wherein thesolution is irradiated with an electron beam having an acceleratingvoltage of about 2 mev.

6. A radiation chemical process as claimed in claim 1 wherein thesolvent is a dry organic liquid.

7. A radiation chemical process as claimed in claim 6 wherein antimony(III) chloride is dissolved in the dry organic liquid and antimonyprecipitates from the solution during irradiation.

8. A radiation chemical process as claimed in claim 1 wherein thesolvent is water which forms hydrogen atoms, hydrated atoms, andhydroxyl radicals during irradiation.

9. A radiation chemical process as claimed in claim 8 wherein thesolvent contains a hydroxyl radical scavenger.

10. A radiation chemical process as claimed in claim 9 10 wherein thesolvent contains hydroxyl radical scavengers selected from the groupconsisting of primary alcohols, secondary alcohols, polyhydroxylalcohols, and aldehydes.

References Cited UNITED STATES PATENTS 1/1963 Bown et a1 204-157.1 H9/1963 Ruskin 204--157.l H

HOWARD S. WILLIAMS, Primary Examiner

